The client is demonstrating signs and symptoms of digoxin toxicity. The antidote for cardiac digitalis glycoside toxicity is:

A) Cough:
Cough is more commonly associated with angiotensin-converting enzyme (ACE) inhibitors, such as enalapril or lisinopril, rather than with beta blockers. ACE inhibitors can cause a persistent dry cough due to the accumulation of bradykinin. Beta blockers do not generally have a direct effect on causing cough, so this is not a typical side effect of beta blockers.

B) Hypotension:
Hypotension (low blood pressure) is a common and well-documented side effect of beta blockers. Beta blockers, such as metoprolol, atenolol, and propranolol, work by blocking beta-adrenergic receptors, leading to a reduction in heart rate and the force of heart contractions, which can lower blood pressure. In patients with already low blood pressure or those receiving other antihypertensive medications, this effect may be more pronounced and could lead to symptomatic hypotension, such as dizziness or lightheadedness.

C) Anxiety:
Anxiety is not a common side effect of beta blockers. In fact, beta blockers are sometimes prescribed to manage symptoms of anxiety, particularly for physical symptoms like palpitations and tremors. However, anxiety may worsen in some individuals due to other factors, such as the psychological impact of dealing with heart disease, but this is not a typical side effect of beta blockers.

D) Elevated heart rate:
Beta blockers work to decrease heart rate by blocking the effects of adrenaline (epinephrine) on beta-adrenergic receptors. This leads to a slower heart rate and reduced workload on the heart. Therefore, elevated heart rate is not a common side effect of beta blockers. In fact, if the heart rate becomes too low (bradycardia), this can be a concerning side effect, but it is the opposite of an elevated heart rate.

A) A headache indicates tolerance to the medication:
A headache does not indicate tolerance to nitroglycerin. Tolerance typically refers to the need for increasing doses to achieve the same therapeutic effect, which is more common with medications like nitroglycerin when used chronically.

B) It sounds as if you are allergic to this medication:
While headaches are a common side effect of nitroglycerin, they are not an allergic reaction. Allergies typically cause symptoms such as rash, itching, or swelling, and are not typically associated with nitroglycerin use. Therefore, attributing the headache to an allergy would be inappropriate.

C) Your headache is probably a result of anxiety about the chest pain:
While anxiety can contribute to physical symptoms like headaches, it is not the most likely cause in this case. Nitroglycerin causes vasodilation, which can lead to headaches as a common side effect. Given that the headache occurred shortly after taking the medication, it is much more likely that the headache is a direct result of the nitroglycerin rather than anxiety about the chest pain.

D) A headache is a common adverse effect of this medication, but it will probably occur less often over time:
Headaches are a well-known and common side effect of nitroglycerin due to its vasodilatory effect, which can cause blood vessels in the head to expand, leading to a headache. The nurse's response is appropriate because it reassures the client that the headache is a typical reaction and that it often becomes less frequent with continued use. The nurse should also remind the client to take the medication as prescribed, and if the headache persists or worsens, they should notify their healthcare provider.